The invention relates to position control systems of the discontinuous feedback type.
Although the invention disclosed herein can be used in a variety of control applications, it has particular utility as a system for aiming a positionable weapon such as a mobile rocket launcher, and then repetitively reaiming the weapon after firing each shell or rocket. Mobile weapons, such as the subject rocket launcher, are designed to be moved from site to site such as from a concealed location to a firing location, and upon arriving at each new firing site, the weapon must be capable of being rapidly positioned, aimed and fired. Moreover, after each round is fired, the weapon must be rapidly reaimed to correct for shifts in its positioning that result from the recoil or other transient reaction to the launched rocket or fired shell.
Known closed loop control systems having continuous feedback between the actual position of the controlled mechanism and the desired position commanded by an input signal, require an excessive amount of energy, usually in the form of electrical power, to drive the mechanism at full power consuming levels, continuously until the error signal has been nulled. Thus, the power drain is substantial, even when only small deviations remain between the actual and desired positions of the mechanism. For an electromechanical system of a size and mass suitable for positioning a large, heavy rocket launcher or artillery piece, the substantial inertia and friction forces associated with aiming the weapon require exceptionally high levels of electrical power to achieve even small position corrections.
Furthermore, in a control system that must be successively activated after each fired round in order to reaim the weapon due to physical displacement caused by the recoil, the high level power consumption of a continuous feedback control system is multiplied by the number of times that the weapon must be reaimed during a multiple round firing sequence.
Also, continuous feedback control systems otherwise suitable for the foregoing purpose, commonly involve circuitry of such complexity that reliability, repair and replacement become factors which significantly detract from their overall effectiveness. Usually, as in the case of the embodiment of the invention disclosed herein, the positioning system will involve at least two axes of positionable movement. To develop a control system of the continuous feedback type for controlling two or more axes, additional complexities are encountered in providing a system which is immuned to cross-coupling of signals between the separately controlled axes. Cross-coupling of control signals can be minimized to a certain extent by positioning the separate axes in succession. However, this increases the amount of time needed to initially aim the weapon and to reaim the weapon after firing each round.
Accordingly, one object of the invention is to provide a control apparatus and method for positioning a controlled mechanism characterized by the capability of accurately and rapidly positioning the mechanism while consuming substantially less power than required to operate a closed loop, continuous feedback control system of comparable response time and final position accuracy.
Another object is to provide such an apparatus and method for aiming and, in succession, reaiming a rocket launching or artillery weapon, wherein the reduced power consumption is particularly beneficial because of the need to reaim the weapon after each round is fired.
Another object of the invention is to provide such an apparatus and method suitable for use in controlling two or more positionable axes of a weapon aiming mechanism, in which the degree of cross-coupling of control signals between the separate axes is reduced to a negligible amount. A related object is to provide such minimal cross-coupling of signals between the controls that govern the axes of movement such that two or more axes can be controlled concurrently to obtain a final positioning of the weapon in the least amount of time.
Another object of the invention is to provide a control system of the above-characterized type, which is capable of achieving considerable accuracy in the aiming of the weapon without involving the complexities and inherent reliability and servicing problems of a continuous feedback positioning system.